Where Is Micro Displacement Setting Both/True/Bump In Blender 2.8
I had a similar problem and found a solution that may help you. 


Navigate to the Material Properties tab.
Within the Material Properties scroll down to a sub-setting titled Settings.
In settings change the displacement type from Bump to Displacement and Bump.


This seems to be the Blender 2.8 equivalent of the "True" setting.